Gripping jaws for gripping sheet metal



May 31, 1966 s. M. DoLNr-:Y 3,253,448

G GRIPPING SHEET META Fil Jun i n' Ml 5 |I lll d WNVITOR. BY

j j ATMP/V94 May 31, 1966 s. M. DOLNEY 3,253,448

GRIPPING JAWS FOR GRIPPING SHEET METAL Filed June l5, 1962 4 Sheets-Sheet 2 V l M* lk W65) /M' M" M 5 M l i? 6 f May 31, 1966 s. M. DLNEY 3,253,448

GRIFFIN@ JAWS FOR GRIPPING SHEET METAL Filed June 13, 1962 4 Sheets-Sheet 5 INVENTOR.

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May 31, 1966 s. M. DOLNEY GRIPPING JAWS FOR GRIPPING SHEET METAL Filed June 15, 1962 United States Patent O 3,253,448 GRIPPIN G JAWS FUR GRIPPING SHEET METAL Stanley M. Doiney, Parma, (lhio, assigner to The Cyril Bath Company, Solon, Ohio, a corporation of Ohio Filed June 13, 1962, Ser. No. 202,153 9 Claims. (Cl. 72-305) This invention relates to` gripping jaws for gripping opposite aligned faces of a portion of sheet metal stock for exerting tension thereon for stretching the stock.

The invention is described herein as employed in stretch forming apparatus such as disclosed in U.S. application of Cyril J. Bath, Serial No. 173,310, filed February 14, 1962, now Patent No. 3,116,780 and entitled Prestretch Fixture and Combination Thereof with Drawing Die Press, its use in other types of apparatus, such as that disclosed in U.S. Letters Patent No. 2,514,930, issued July l1, 1950, being apparent from the illustrative example.

Heretofore, in stretch forming of sheet metal stock, the

practice has been to grip opposite end margins of a length of stock in suitable gripping jaws and then to exert tension on the stock by moving the jaws relatively apart from each other endwise of the stock. Considerable difliculty has been experienced in obtaining a firm enough grip on the stock to prevent slippage of the gripped portion of the stock relative to the jaws in the direction of pull on the gripped portion, which direction is along the plane of the portion gripped between the jaws.

Heretofore those surfaces of the jaws which engage the opposite face portions of the stock have been roughened, generally by providing on each of the gripping faces of the jaws a multiplicity of very small teeth distributed uniformly over the gripping area. Generally the teeth of each jaw are diamond shaped, being formed by crisscrossing two groups of facial serrations or V-shaped grooves, the grooves of each group being parallel to each other crisscrossing the grooves of the opposite group. The resultant diamond shaped teeth are pyramidal with sharp peaks. This type of gripping surface is common -in the jaws of many types of gripping devices, such as the jaws of vises, clamps, and the like.

However, after a certain amount of use, the peaks tend to wear down and round off. When the peaks lose their sharpness, the effectiveness of the teeth in preventing slippage of the stock is reduced. Furthermore, the grooves between the teeth ll with foreign matter, such as accumulated grease, dust, and metal scraped by the teeth from slipping stock, and the like, further'reducing their effectiveness to prevent or reduce slippage. Again, since the teeth are small relative to the manufacturing tolerances f permitted in the relatively movable clamping mechanisms of the jaws, it is not feasible to maintain the teeth on one jaw in precisely aligned or staggered relation to those of the other jaw. As a result, the resistance to slippage does not remain constant.

Due to variations in the grip, attempts' have been made to provide for stretch forming machines jaws of which the gripping faces are roughened by parallel grooves and ridges which form sharp elongated teeth of generally triangular cross section extending at right angles to the direction of tension on the portion of the stock gripped between the jaws. However, thicker steel sheets and newer alloys now being stretch formed require ever more heavy gripping jaw pressure to prevent slippage. With sharp ridge shaped teeth on both gripping faces extending transvedge of the gripped sheet stock or pair of faces.

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versely of the direction of pull on that part of the metal between the jaws, the increased pressure causes the teeth to embed in the metal stock and acts as shears which cut partially through the metal. Frequently they cut so deeply that there is insuflicient cross sectional area of stock to withstand the tension applied. As a result, the weakened portions of the stock frequently tear apart before tension of the stock adequate for stretching is developed.

In order to provide jaws of improved gripping qualities, the jaws of the present invention are provided with gripping faces such that each face of the faces of a pair of companion jaws has a row of generally parallel elongated gripping ridges or teeth. In the plane of the gripped portion of the sheet stock, the ridges of each row are spaced laterally of their length from each other. Each ridge is oblique to the length of its row and to the direction of tension applied on that portion of the sheet stock gripped between the gripping faces. The ridges on one face extend, in the direction of their length, transversely of those of the other face, the obliquity of the ridges of one face being such that the ridges slope from front' to rear of the faces in a direction away from one lateral edge of the gripped sheet stock or pair of faces, and the obliquity of the ridges of the other face being such that they slope from front to rear in a direction toward the same lateral Thus the projected patterns of the ridges of the aligned faces of the jaws, in superposed relation on a plane parallel to the faces, is a crisscross pattern when the jaws are in clamping position. Generally the angles to the direction of pull on the gripped portion of the stock made by the ridges of one face are equal in degrees to, but opposite to, those made by the ridges of the other face. Preferably, these angles are 45 each, so that the projected crisscross pattern of the ridges is one in which the ridges of one face cross those of the other face at and the direction of pull through the intersections of each crisscross bisects the 90 angle thereof. This particular angle is desirable because the direction of shear of metal under tension applied in a given direction is about 45 to that direction, and hence a multiplicity of ridges extend substantially normal to the lines of shear of the metal sheet and accordingly assure a firm grip for resisting slippage.

Various specific objects and advantages of the present invention will become apparent from the following description, wherein reference is made to the drawings, in which:

FIG. 1 is a diagrammatic front elevation of a press with a pair of stretch forming assemblages employing the jaws of the present invention installed for operation;

FIG. 2 is a fragmentary front elevation of the stretch forming gripping head ofthe right hand assemblage illustrated on the line 2-2 of FIG. 1;

FIG. 3 is a vertical sectional view taken on the line 3 3 of F IG. 2;

FIG. 4 is a top plan view of the bottom jaw and its holder;

FIG. 5 is an enlarged vertical sectional view taken on the line 5--5 in FIGJ4;

FIG. 6 is an enlarged fragmentary top plan view showing the teeth of the gripping face of the bottom jaw;

FIG. 7 is a fragmentary vertical sectional view through the portion of the bottom jaw illustrated in FIGS. 4 and 6 showing the crossV sectional profile of the gripping ridges;

FIG. 8 is a top plan view of the top jaw and holder;

FIG. 9 is an enlarged sectional view taken on the line 9-9 in FIG. 8;

FIG; 10 is an enlarged fragmentary top plan view of the upper jaw showing the position of the gripping ridges;

FIG. 11 is a vertical sectional view taken on the line 11-11 of FIGS. 8 and 10, showing the cross sectional prole of the gripping ridges;

FIG. 12 is a fragmentary view showing the crisscross pattern made by projection of the ridges of the upper and lower jaws on a plane parallel tothe jaw faces; and

FIG. 13 is a fragmentary diagrammatic side elevation showing the use of the jaws and gripping devices for stretching a sheet of metal in a direction disposed normal to the plane of the gripping faces ofthe jaws.

Referring rst to FIG. 1, the jaws are shown embodied in a stretch forming assemblage used in connection with the apparatus more fully described in the above identitied application wherein a sheet of stock is stretched generally horizontally. For brevity, the jaws are described herein in the operating position therein illustrated.

As therein more fully described, the assemblages are installed in a press 1 having a horizontal bed 2 and upright guides 3 which support a vertically reciprocal ram 4. A male drawing die 5 is installed on the bed in alignment with a complementary female drawing die 6 carried by the ram. The ram is moved upwardly and downwardly by piston and cylinder assemblages 7 including cylinders 8 in which pistons 9 are reciprocable, the pistons being connected by piston rods 10 to the ram for raising and lowering the ram.

For stretching the sheet preparatory to forming between the dies 5 and 6, two stretch forming assemblages 11 are provided on the bed. These assemblages are duplicates of each other and are arranged to engage opposite ends of the length of stock S for applying tension thereto independently of the drawing tension that might be imposed by the operation of the dies 5 and 6. Various means may be utilized for moving the jaws of the assemblages relatively away from each other for exerting the tension on the stock, but for purposes of illustration the means shown are those disclosed in the above application. As there illustrated, each assemblage includes a gripping stretch head 12 mounted on a suitable carriage 13 which is arranged on a support 14 for movement endwise of the length of stock S. The support 14 is rigidly secured on the bed 2 and is provided with upwardly facing trackways l5 on which the carriage 13 may travel toward and away from the path of the dies 5 and 6. The carriage 13 is provided at its forward end with rollers 16 which ride on the trackways 15. At its opposite end, the carriage 13 is connected to one end of a link 17 by means of a pivot 18. The opposite end of the link 17 is connected by a pivot 19 to the support 14. Pivotally connected to the link intermediate the pivots 18 and 19, by means of a pivot 20, are piston rods 21 of pistons 22 which are operable in hydraulic cylinders 23. Controlled pressure fluid for stretching the stock is supplied to the cylinders by a suitable solenoid operated reversing valve 24 from a pump 25 driven by a motor 26. As described in the above application, the link 17 is practically coextensive in width with the length of the gripping head 12 in the direction transversely of the sheet stock. The head 12 is yieldably urged away from the dies by means of its piston and cylinder assemblages so as to exert tension on the stock, and is returned to starting position thereby.

For gripping the stock, each head 12 carries a pair of gripping jaws which exend the width of the piece of stock to be gripped and which have opposing aligned faces for engaging the opposite faces of the stock. In the form illustrated, the jaws are comprised of an upper jaw 30 and a lower jaw 31. The jaw 30 is carried on a holder 32 and a clamping face plate 33 is xedly secured to the jaw and faces downwardly. The plate 33 is at least coextensive with the width of the strip to be gripped. The jaw holder 32 is movably supported by suitable bolts cesses 54 and 55 in the plate holders.

34 on a backup guide 35. The backup guide has a downwardly facing wedge cam surface 36 co'operable with an upwardly facing wedge surface 37 on the jaw holder 32. The bolts 34 secure the holder to the backup guide 35 for sliding movement forwardly and rearwardly along the wedge surfaces. The wedge surfaces 36 and 37 are arranged so that upon forward movement of the holder 32 toward the dies the upper jaw 30 is forced to move downwardly. Correspondingly, the lower jaw 31 comprises a holder 42 and a clamping face plate 43 fixedly secured thereto. The holder is secured by bolts 44 to a backup guide 45 for sliding along a wedgesurface 46 thereon. The surface 46 cooperates with a complementary wedge surface 47 on the holder 42. The holders 32 and 42 may be thus constrained by keys 48 and 49, respectively, for movement lineally forwardly and rearwardly. It is apparent with this arrangement that forward movement of the jaws moves their clamping plates 33 and 43 toward each other and into wedged'clamping engagement with the opposite face portions of the stock S. Once a length of stock is gripped therebetween sufficiently to exert any tension on the stock, further tension on the stock tends to pull the jaws forwardly toward theopen end of the head and cause even tighter wedge clamping engagement.

However, it is generally desirable that the jaws be moved forwardly for clamping pressure by suitable power means. For this purpose a row of piston and cylinder assemblages are provided. Each assemblage includes a cylinder 50 arranged in the head and accommodating a piston 51 having a rod 52 on the outer end of which is a connector 53. The connectors engage in suitable re- Pressure tluid is supplied through suitable reversible pressure lines 56 to opposite sides of the pistons 51 for advancing and retracting the jaws selectively. Pressure fluid is supplied to the cylinders 50 through a suitable reversing valve 58 from a pressure pump 59 driven by a motor 60. The structure thus far described is fully disclosed in the above application.

As mentioned, the gripping faces of the jaw, with which the present invention is concerned, are provided on the plates 33 and 43. Referring next to FIGS. 8 through 11, the top plate 33 has its bottom gripping face serrated with parallel V-shape grooves to provide a plurality of parallel ridges 62 arranged side by side in a row and spaced laterally of their lengths from each other. The row extends transversely of the direction of tension applied on that portion of the stock gripped between the plates 33 and 43. Preferably, for ease in manufacture, the ridges are linear and are arranged closely adjacent to each other and are uniformly distributed along the length of the row and are triangular in vertical cross section. The ridges, however, are oblique relative to the direction of tension on that portion of the sheet gripped between the plates.

For example, referring to the upper jaw in FIG. 8, the plate 33 has ridges 62. The direction of tension is indicated by the arrow 63 and each of the ridges extends, endwise of its length, oblique to that direction at an angle A.

Referring to the lower jaw in FIG. 4, the plate 43 is provided with ridges 64 which may be the same shape and configuration as the ridges 62. However, the ridges 64 extend at an angle B to the direction of tension which is indicated bythe arrow 65.

Referring to FIG. l2, it is to be noted that, when viewed from the top, the ridges 62 of the top jaw extend, endwise of their lengths, oblique to the direction of tension indicated by the arrow 63 such that, beginning at one lateral edgeof the plates or sheet, they slope away from that edge from front to rear of the jaws. However, the ridges 64 of the bottom jaw slope toward said one lateral edge in a direction from front to rear of the jaws. Thus the projected pattern of the ridges of the top and bottom plates is one in which the ridges of one plate crisscross those ofthe other plate.

Preferably the angles A and B are 45 so that the lengths of the ridges of the upper jaw extend at right angles to the lengths of the ridges of the bottom jaw. The 45 angles are preferred because of the tendency of metal stock under tension to shear along surfaces at an angle of 45 to the direction of the tension above yield.

This arrangement assures that at least one of the shearing surfaces will be at right angles to the ridges of one plate or the other. Furthermore, it is preferable that the angles A and B be equal, even if not 45, so that the reactionary forces tending to cause the sheet to slip edgewise in either direction will be counteracted by an opposite reactionary force imposed by the ridges of one or .the other of the jaws.

It has been found `that with clamping faces of this character, much higher tension can be applied to sheet stock without slippage of the jaws relative to the 4sheet and without appreciable weakening of the gripped portion of the sheet. With the present jaws, no observable slippage occurs. This is very beneficial in stretch forming apparatus in that when a sheet is being stretch formed, slight slippage of the jaws can result in a sudden jerk on the sheet which can cause temporary reduction of the tensioning force followed by the reapplication of the l tensioning force at a level somewhat above normal due to inertial forces. Such an interruption and change in force raises the elastic limit and changes the physical characteristics of the sheet. Furthermore, any such slippage makes difficult the precise measuring and forming which would otherwise be obtained.

While the ridges herein shown are of a linear pattern, they could be of curvilinear shape with a general crisscrossing effect. However, the endwise curvilinear shapes are much more difficult to form and furthermore, such curves generally have components which areA parallel lto the direction of tension, in which case the resistance to slippage is reduced.

The present jaw face structure i-s one that is particularly useful in connection with the newer alloys which have an elastic limit and yield point considerably above that of the more conventional steels and the like. Also, the jaws and face plates lend lthemselves to ready manufacture. For example, the same plate and jaw can be used for a top jaw of any pair, or a bottom jaw. For example, when the bottom plate is facing upwardly, if the top plate is also positioned to face upwardly, all of the ridges of both plates are parallel to each other in the same direction and thus can all be set up and machined in the same operation. The crisscross eect is obtained merely by inverting the top jaw and its plate, because thereupon the top ridges, theretofore, parallel with those of the bot-tom jaw, then extend at right angles thereto. This can readily be seen by making a plurality of parallel lines on a piece of paper oblique to the length of paper and then folding the paper along a line transversely of its length, and passing light therethrough so as to view the then superposed lines.

In the structure thus far described, the direction of tensioning of the ungripped portion of the sheet is in the plane of the gripped portion. In FIG. 13, a head 70 is shown. This head is a side gripping type having jaws 71 and 72 so arranged as to grip a margin Sm, of a length of stock S, which extends at 90 to the length of the stock S and the direction of tension of the ungripped portion, which direction is indicated by the arrow 73.

However, the same type of resistance to slippage is provided, as the gripped por-tion Sm is urged by the tensioning force on the Isheet in the plane of the jaw faces, in the direction indicated by the arrow 74, which is forwardly of the jaws or heads.

Having thus described by invention, I claim:

1. In a stretching machine, a frame, gripping heads mounted thereon for movement relatively toward and away from each other and adapted for clamping engagement with opposite margins of a sheet of metal stock for stretching the sheet along the dimension from one of .6 said margins to the opposite margin when the heads are moved relatively apart, whereby the margin of stock gripped by each head would be urged to slip in a forward direction relative thereto, power means for effecting relative movement of the heads toward and away from each other, selectively, each head including a pair of clamping jaws, means on the heads, respectively, connecting each pair of jaws to its associated head for movement to clamping and release-d positions, respectively, and for holding each pair in a fixed position relative to its associated head when the jaws are in the clamping position, power means for moving the jaws into clamping position, the jaws of each pair having gripping faces, respectively, which are aligned in face to face spaced relation to each other when the jaws are in a clamping position, each gripping face of a pair having a forward edge and a rear edge and having elongated gripping ridges spaced transversely of their length from each other, said ridges extending, endwise of their own length, oblique to the said forward direction, the ridges on one face of each pair of jaws sloping, from the forward edge to the rear edge, away from one lateral edge of the pair of faces, and the ridges on the other face of each pair sloping, from the forward edge to the rear edge, toward said one lateral edge of the pair of faces, so that the superposed projected patterns of the ridges of the two aligned faces on a plane generally parallel to the aligned faces are in a crisscross relation to each other when the faces are in gripping relation.

2. A gripping head according to claim 1 wherein the angle at which the ridge crosscross at each intersection is substantially bisected by a line through the intersection parallel to the direction of movement of the heads.

3. The clamping head according to claim 2 wherein each angle of Obliquity of -the ridges of one jaw from front yto rear is about from Vsaid lateral edge and each angle lof Obliquity of the ridges of the other jaw from front to rear is about 45 to the same lateral edge.

4. The clamping head according to claim 1 wherein the ridges of the face of each jaw of a pair are preferably lineal parallel ridges of V-shaped cross section, with their peaks adjacent the face of the `other jaw of the pair, and are closely spaced, laterally -of their lengths, with respect to each other.

5. The clamping head according to claim 1 wherein the ridges preferably have a depth of .036 inch and ytheir peaks are spaced apart about .062 inch.

6. The clamping head according to claim 1 wherein the adjacent faces of adjacent ridges of each face preferably intersect each other at a base angle of about 81.

7. The clamping head according to claim 1 wherein each ridge is lineal throughout its length.

8. In a stretching machine, a frame, gripping heads mounted thereon for movement relatively toward and away from each other and adapted for clamping engagement with opposite margins of a sheet of metal stock for stretching the ysheet along the dimension from one of said margins lto the opposite margin when the heads are moved relatively apart, whereby the margin of the stock gripped by each head would be urged to slip in a forward direction relative thereto, power means for effecting relative movement -of the heads toward and away from each other, selectively, each head including a pair of clamping jaws, means on the heads, resepectively, connecting each pair of jaws -to its associated head for movement to clamping and released positions, respectively, and for holding each pair in a fixed position relative to its associated head when the jaws are in said clamping position, power means for moving the jaws into clamping position, the jaws of each pair having gripping faces, respectively, which are aligned in face to face spaced relation to each other when the jaws are in a clamping position, each gripping face of a pair having a forward edge and a rear edge and having elongated gripping ridges spaced transversely of their length from each other, said ridges on at least one face extending, endwise of their own length, oblique `to one lateral edge of the pair, and the ridges on the other face of the same pair being at an angle to said lateral edge different from the angle of Obliquity of the ridges of said one face so -that the superposed projected patterns of the ridges of the two aligned faces on a plane parallel to the aligned faces are in a crisscross relation to each other when the faces are in gripping relation.

9. A gripping head according to claim 8 wherein the ridges of each jaw are relatively sharp peaked.

References Cited by the Examiner UNITED STATES PATENTS Rust 81-186 Griswold 81'-186 Tinley 153-35 St. Pierre 81-186 Hill et al. 153-35 CHARLES W. LANHAM, Primary Examiner. 0 

1. IN A STRETCHING MACHINE, A FRAME, GRIPPING HEADS MOUNTED THEREON FOR MOVEMENT RELATIVELY TOWARD AND AWAY FROM EACH OTHER AND ADAPTED FOR CLAMPING ENGAGEMENT WITH OPPOSITE MARGINS OF A SHEET OF METAL STOCK FOR STRETCHING THE SHEET ALONG THE DIMENSION FROM ONE OF SAID MARGINS TO THE OPPOSITE MARGIN WHEN THE HEADS ARE MOVED RELATIVELY APART, WHEREBY THE MARGIN OF STOCK GRIPPED BY EACH HEAD WOULD BE URGED TO SLIP IN A FORWARD DIRECTION RELATIVE THERETO, POWER MEANS FOR EFFECTING RELATIVE MOVEMENT OF THE HEADS TOWARD AND AWAY FROM EACH OTHER, SELECTIVELY, EACH HEAD INCLUDING A PAIR OF CLAMPING JAWS, MEANS ON THE HEADS, RESPECTIVELY, CONNECTING EACH PAIR OF JAWS TO ITS ASSOCIATED HEAD FOR MOVEMENT TO CLAMPING AND RELEASED POSITIONS, RESPECTIVELY, AND FOR HOLDING EACH PAIR IN A FIXED POSITION RELATIVE TO ITS ASSOCIATED HEAD WHEN THE JAWS ARE IN THE CLAMPING POSITION, POWER MEANS FOR MOVING THE JAWS INTO CLAMPING POSITION, THE JAWS OF EACH PAIR HAVING GRIPPING FACES, RESPECTIVELY, WHICH ARE ALIGNED IN FACE TO FACE SPACED RELATION TO EACH OTHER WHEN THE JAWS ARE IN A CLAMPING POSITION, EACH GRIPPING FACE OF A PAIR HAVING A FORWARD EDGE AND A REAR EDGE AND HAVING ELONGATED GRIPPING RIDGES SPACED TRANSVERSELY OF THEIR LENGTH FROM EACH OTHER, SAID RIDGES EXTENDING, ENDWISE OF THEIR OWN LENGTH, OBLIQUE TO THE SAID FORWARD DIRECTION, THE RIDGES ON ONE FACE OF EACH PAIR OF JAWS SLOPING, FROM THE FORWARD EDGE TO THE REAR EDGE, AWAY FROM ONE LATERAL EDGE OF THE PAIR OF FACES, AND THE RIDGES ON THE OTHER FACE OF EACH PAIR SLOPING, FROM THE FORWARD EDGE TO THE REAR EDGE, TOWARD SAID ONE LATERAL EDGE OF THE PAIR OF FACES, SO THAT THE SUPERPOSED PROJECTED PATTERNS OF THE RIDGES OF THE TWO ALIGNED FACES ON A PLANE GENERALLY PARALLEL TO THE ALIGNED FACES ARE IN A CRISSCROSS RELATION TO EACH OTHER WHEN THE FACES ARE IN GRIPPING RELATION. 